Table of contents
- Types of cyber attacks
- Clear signs of a cyber attack: examples and tools
- Which of these is a clear sign?
Cyber attacks are an ever-evolving threat that can affect companies, institutions, and individuals alike. No one is truly immune.
The ability to quickly recognize the signs of a cyber intrusion is now essential to minimize damage, protect data, and safeguard digital infrastructure. In this article, we explore the main types of cyber attacks and identify the clear signs that indicate a system has been compromised.
Types of cyber attacks
Cyber attacks take many forms, each with its own methods and objectives. Understanding them is the first step in defending against them.
- Phishing
Among the most widespread techniques, phishing uses deception to obtain login credentials or sensitive information. It often appears as an email from a seemingly trustworthy source, complete with official-looking logos and signatures. These messages typically contain malicious links or attachments designed to steal data or install malware.
- Malware
Malware includes various forms of malicious software — viruses, worms, trojans — that infiltrate IT systems, compromise files, steal information, or provide unauthorized remote access. It typically spreads via infected email attachments, downloads from untrustworthy websites, or compromised USB devices.
- Ransomware
A particularly dangerous form of malware, ransomware encrypts user data and demands a ransom — usually in cryptocurrency — to release the decryption key. Without clean backups, victims may face severe operational and financial consequences.
- Man-in-the-Middle (MitM) attacks
In a MitM attack, the hacker silently intercepts communication between two parties to steal or manipulate data. This often occurs on unsecured public Wi-Fi networks or through compromised routers that allow attackers to alter traffic in transit.
- DoS and DDoS attacks
Denial of Service (DoS) and Distributed Denial of Service (DDoS) attacks aim to make websites or online services unavailable by flooding them with excessive requests. DDoS attacks are usually executed using botnets — networks of infected devices — to intensify the impact and obscure the origin.
- IP-based attacks
Using an exposed IP address, cybercriminals can scan ports, attempt brute-force logins, or exploit vulnerabilities to gain unauthorized access. These attacks are often the first step in more complex intrusion strategies.
Clear signs of a cyber attack: examples and tools
Quickly recognizing a cyber attack in progress can be the difference between prompt recovery and a full-scale breach. Below, we’ll explore each clear sign in depth, providing realistic scenarios, practical tips, and code snippets where applicable.
Sudden system slowdowns
A drastic drop in performance can indicate malware consuming CPU or RAM for hidden tasks.
Example
You’re only running a browser, but your CPU usage is over 90%.
Check on Windows (PowerShell):
Get-Process | Sort-Object CPU -Descending | Select-Object -First 10Check on Linux:
top
# or
ps aux --sort=-%cpu | headIf you see unknown or suspicious processes, run a full malware scan.
Unusual popups and Windows
Spyware or adware may cause popups, even with your browser closed.
Example
Popups urging you to “remove threats” or click to claim a prize.
Technical tip:
Check Startup Programs (Windows):
wmic startup get caption, commandYou can also use Autoruns from Microsoft Sysinternals to identify and disable suspicious autostart entries.
- Unauthorized File Modifications
Ransomware often encrypts and renames files.
Example
Your .docx files are now .docx.locked or .encrypted.
Python code to detect recent file changes in a folder:
import os, time
path = "C:/Users/YourName/Documents"
before = {f: os.path.getmtime(os.path.join(path, f)) for f in os.listdir(path)}
time.sleep(10) # wait 10 seconds for this test
after = {f: os.path.getmtime(os.path.join(path, f)) for f in os.listdir(path)}
modified = [f for f in before if before[f] != after.get(f)]
if modified:
print("Modified files:", modified)Unusual network traffic
Example
Your system sends data to a suspicious IP (e.g., in another country) over an unfamiliar port.
Check connections on Windows:
netstat -ano | findstr ESTABLISHEDOn Linux:
sudo lsof -i -n -P | grep ESTABLISHEDAdvanced tools: use Wireshark, tcpdump, or Zeek to monitor traffic in real time and spot data exfiltration.
Antivirus or Firewall disabled
Example
You receive a notification that your antivirus or firewall has been turned off, and you can’t re-enable it. Some malware disables protection to operate undetected.
PowerShell check:
(Get-MpComputerStatus).AntivirusEnabled
(Get-NetFirewallProfile).Enabled
Unknown programs installed
If you find software you didn’t install, it may be part of a remote access toolkit (RAT) or other malicious implant.
Example
A new app appears named update_service.exe that was never installed manually.
List programs (Windows):
Get-WmiObject Win32_Product | Sort-Object NameOn Linux:
dpkg --get-selections | grep -v deinstall- Access from unusual locations
Logins from unusual locations If your accounts are showing logins from unusual geographic locations, they have probably been compromised.
Example
You receive a security alert: “Login from São Paulo, Brazil,” but you’re in New York.
Technical tip:
Enable two-factor authentication (2FA) and monitor account access logs in:
- Google Account → Security → Recent activity
- Microsoft 365 → Security center → Login history
- WordPress → Use plugins like “WP Activity Log”
Emails sent automatically from your account
Example
Friends or coworkers receive strange emails from your address with suspicious links or generic messages.
This means your email account is compromised and used for spamming or malware distribution.
For Gmail Workspace accounts:
- Go to Settings → Security → Account Activity
- Check for suspicious filters, forwarders, or rules
Ransom demands or lock screens
Example
You boot your computer and see a red screen reading:
“Your files have been encrypted. Pay in Bitcoin to recover them.”
This is a classic ransomware attack. Do not restart or pay the ransom. Disconnect from the network immediately and contact a cyber security professional.
Fake antivirus warnings
Example
A full-screen alert says:
“Warning! Your PC is infected. Download Antivirus Pro 2025 now!”
This is likely rogue security software, attempting to trick you into downloading more malware or making a fraudulent payment.
- What to do:
Boot in Safe Mode and use an offline malware scanner like Microsoft Defender Offline.
Which of these is a clear sign?
Not all suspicious behavior points directly to an attack — for example, a slow system could be due to a routine update.
However, unauthorized file changes, disabled antivirus, unexpected installations, and ransom demands are unmistakable indicators of a cyber attack. Taking immediate action can prevent further data loss and service disruption.
Frequently asked questions
- What is a cyber attack and who is at risk?
It’s a malicious action aimed at damaging, stealing, or blocking digital data. Everyone — from individuals to corporations — is at risk. - Are system slowdowns always a sign of an attack?
Not always, but persistent slowness accompanied by other symptoms deserves investigation. - What should I do if I receive a ransom demand?
Don’t pay. Disconnect the device from the network, contact a professional, and check for clean backups. - How can I protect against phishing?
Always verify sender addresses, avoid clicking suspicious links, and use two-factor authentication. - What are the most common threats today?
Phishing, ransomware, DDoS, spyware, and unauthorized system access. - Can public Wi-Fi expose me to spying?
Yes. Unsecured networks are easy targets for MitM attacks that intercept your data. - Is free antivirus software enough?
Usually not. For full protection, a comprehensive security suite is recommended. - How can I tell if my IP is under attack?
By monitoring network traffic using advanced firewalls or port scanning tools. - Are there visible signs on a hacked website?
Yes: slow loading times, redirect issues, altered content, or browser warnings. - How important is cyber security training?
Crucial. Educated users are the first line of defense against cyber threats.
